Last year the hottest on record for U.S. — NOAA

The United States experienced its warmest year yet in 2012, with the highest surface temperatures since record keeping began in the mid- or late 1800s, according to the annual “State of the Climate” report released today.

Last year also ranked either eighth or ninth in highest surface temperatures worldwide, depending on which of the four data sets considered by the report were used. The report, posted online today by the American Meteorological Society, was authored by an international group of nearly 400 scientists, with those from the National Oceanic and Atmospheric Administration’s National Climatic Data Center serving as its lead editors.

“Earlier this summer, the president of the United States called upon agencies like NOAA to develop strategies to help make decisionmakers prepared for the impacts of a changing climate,” acting NOAA Administrator Kathryn Sullivan said on a call with reporters. The report will inform city planners, managers of land and water resources, and others about climatic trends they can incorporate into their planning, she said.

Today’s is the 23rd “State of the Climate” report, “and every year we add new chapters to this historical account, allowing us to compare the Earth’s climate from year to year and over decades,” Sullivan said.

This year’s chapter shows a continuation of longer-term trends in climate change, including accelerated sea-level rise, warmer oceans, more atmospheric humidity and changing weather patterns. Polar sea ice coverage has also shifted dramatically since the middle of the last century, and ice sheets are diminishing in the Arctic, Greenland and Antarctica, it said.

The report found that the 2012 globally averaged sea surface temperature was higher than the 1981-2010 average, and the annual temperatures have been above that average for a decade.

Thomas Karl, director of NOAA’s National Climatic Data Center, said it was important to continually add to the world’s understanding of how the climate is changing. But he emphasized that the report does not try to attribute any changes to human or natural activity.

“It does not try to explain why we are seeing what we’re seeing,” he said. “So this report is focused on what are the observations telling us, and are they telling us a story that we think makes sense in a holistic picture of a changing planet?”

But while it did not make the link between industrial emissions and a shifting climate, the report did note that global greenhouse gas emissions were on the rise last year. Global mean CO2 reached 392.6 parts per million, an increase of 2.1 ppm over 2011 levels. Global mean levels of methane, which is 21 times as climate-forcing as CO2, reached 1,808.5 parts per billion last year, up 5.1 ppb from the previous year.